# Pressure in tank

1. Apr 8, 2016

### foo9008

1. The problem statement, all variables and given/known data
in this question , the author stated that the P1 = P atm , but at point 1 , the gas tank is not open to the atmosphere, it is a closed tank . so , is the author wrong ? again , at point 2 , the tank isn't open to atmosphere, why it is P2= P atm ?

2. Relevant equations

3. The attempt at a solution

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2. Apr 8, 2016

### Staff: Mentor

Why might the two pressures be P atm? Can you think of any reason? How does the small diameter hose reach the liquids?

3. Apr 8, 2016

### foo9008

i dont think P1 and P2 = P atm .....

4. Apr 8, 2016

### Staff: Mentor

I understand that. But can you think of any way that they could?

5. Apr 8, 2016

### foo9008

for P1 = P2 = P atm , the tank is not closed?

6. Apr 8, 2016

### Staff: Mentor

Correct. How does the hose enter each tank?

7. Apr 8, 2016

### foo9008

at point 1 , it is immersed in the gas tank , while the point 2 is at the hole only , not completely immersed . What are you trying to tell ?

8. Apr 8, 2016

### Staff: Mentor

I'm pointing out that neither tank is sealed. Both are open to the atmosphere through their filling apertures. The siphon hose does not make an air-tight seal at either opening.

9. Apr 8, 2016

### foo9008

if that is air-tight selaed , then the pressure acting would not be P atm anymore , am i right ?

10. Apr 8, 2016

### Staff: Mentor

Sure. It might start out at P atm at the moment a seal was made though.

But there is no seal mentioned in the problem statement. The assumption is that, as in the real-life situation for siphoning gas in this manner, the hose fits loosely through the gas cap opening and down into the liquid.